This invention relates to a cryosurgical instrument. It relates more particularly to an instrument of this type having a non-electric defrost capability. In such equipment, gaseous refrigerant is conducted via a restriction to the hollow working tip of the instrument whereby tissue in contact with the tip becomes frozen. Thereafter the tip may be warmed to facilitate its separation from the tissue by providing warm refrigerant at the hollow working tip of the instrument.
Several non-electrical methods have been proposed for reheating the working tips of similar instruments. One such method is disclosed in U.S. Pat. No. 3,696,813 and involves restricting or completely closing the exhaust passage from the tip so that refrigerant fluid, still flowing through the restriction raises the pressure within the working tip. Resultantly the gaseous refrigerant begins to condense on the cold surfaces of the tip, the latent heat of condensation thereby warming the tip sufficiently to permits its separation from the tissue.
In another cryosurgical instrument, the cooling of the hollow working tip of the instrument is provided by unseating a flow valve element in the return line located downstream from the tip and simultaneously forming a restrictive orifice at the inlet to the tip by contacting an orifice seat with a moveable conduit. Refrigerant then flows from the source through the orifice and exhausts through the unseated downstream valve. Warming of the tip is accomplished by seating the downstream valve element and simultaneously separating the moveable conduit from the orifice seat thus permitting refrigerant at ambient temperature to flood the hollow working tip.
Still another instrument of this type having a non-electric defrost capability is described in U.S. Pat. No. 3,913,581. That instrument is similar to the first-mentioned one except that during the defrost mode of operation, the hollow tip of the instrument is pressurized from the source of refrigerant through a flow path separate from flow restricting inlet to the tip. In this type, the refrigerant is said to condense on the tip wall more rapidly thereby resulting in a more rapid warming of the tip during the defrost mode of operation.
These prior cryosurgical instruments having a defrost capability all have attendant disadvantages which militate against their wider use and application. More particularly, the instrument described in U.S. Pat. No. 3,696,813 has rather large valves which are mounted in the instrument itself resulting in a large gun-shaped probe that is quite unwieldy and appears threatening to some patients. On the other hand, the instrument having the flow valve in the probe that unseats, requires a moveable conduit and valving that are complex and therefore difficult and expensive to make on a consistently reliable basis. Finally, the instrument embodiments described in U.S. Pat. No. 3,913,581 all have hand or foot-operated valves separate from the instrument itself. Consequently they require separate consoles and extra high pressure hose lines making the overall systems more expensive and also more bulky and difficult to move about. There is no teaching in that patent how the disclosed valve arrangements could be incorporated into the instrument itself without making it large, unbalanced in speculum and generally difficult for the doctor to hold and manipulate during a prolonged or delicate surgical procedure.